Please explain this code that uses std::ignore
c++, c++11
Solution
`set::insert` returns a pair where first is the iterator to the inserted element and second is a bool saying whether the element was inserted.
`std::tie` creates a tuple of lvalue references. When assigned to the result from `insert` it enables you to set the variables in the `tie` to the results of the insert in the return `pair`'s `first` and `second` members.
`std::ignore` is a value that can be assigned to with no effect.
So basically, this code ignores the iterator to the element where `"Test"` was inserted and asigns `inserted` to the `second` member of the pair returned by `set::insert` that indicates whether the an element was inserted.
Problem
I'm reading the documentation on `std::ignore` from cppreference. I find it quite hard to grasp the true purpose of this object, and the example code doesn't do it much justice. For example, in the below code, how and why is `inserted` set to true? It doesn't make much sense to me. ``` #include <iostream> #include <string> #include <set> #include <tuple> int main() { std::set<std::string> set_of_str; bool inserted; std::tie(std::ignore, inserted) = set_of_str.insert("Test"); if (inserted) { std::cout << "Value was inserted sucessfully\n"; } } ``` If someone can explain the code to me, it would be appreciated. Thanks.